The Staphylococci: Isolation and Identification

Staphylococci Collectively, the staphylococci and streptococci are referred to as pyogenic (pus-forming) gram-positive cocci Implicated in many different type of infections Skin infections like acne or boils, urinary tract infections , pneumonia, endocarditis, septicemia Staphylococci occur in “grape-like” clusters Staphylococci are part of the normal flora of nasal membranes, hair follicles, skin, and perineum in healthy individuals. At least 40 different species of Staphylococcus Staphylococcus are catalase positive One way to differentiate Staph from Strep

Staphylococcus aureus Produces certain enzymes that help distinguish from non-pathogenic staph Pathogenic enzymes Coagulase: promotes the formation of clots Help seals the organism off from the immune system Enterotoxin: toxin protein that causes food poisoning Leukocidin: protein that destroys white blood cells Hemolysins: enzymes that destroy red blood cells

Coagulase Negative Staphylococci Coagulase Negative Staphyloccocus Make up approximately 40 different species Staphylococcus epidermidis Normal skin flora Can cause severe infections in immunocompromised patients and those with catheters or ports Staphyloccous saprophyticus Normal vaginal flora Implicated in urogenital tract infections

Coagulase TEst Coagulase is an enzyme that causes the fibrin of blood plasma to clot. If test is positive: Staph aureus If test is negative: Coagulase negative Staph

Slide agglutination Latex beads are coated antibodies for Protein A. Protein A is a surface protein found on Staphylococcus aureus If test is positive: Staph aureus If test is negative: Not Staph aureus Note: You cannot say coagulase negative Staph because you have not performed a coagulase test

Streptococci: Isolation and Identification

Streptococci We will look at 2 systems to classify the Streptococci Differ from Staphylococci: Occur in chains Lack the enzyme catalase Can cause mixed infections with Staphylococci Independently can cause: Pneumonia, meningitis, endocarditis, pharyngitis, erysipelas, and glomerulonephritis Fastidious microaerophilic organisms Need extra nutrients for growth More CO2 and less O2 than atmospheric levels We will look at 2 systems to classify the Streptococci Hemolytic patterns antigens associated with the cells –Lancefield classification System

Hemolytic Patterns Hemolysis: Ability of the bacteria to cause lysis of the red blood cells when grown on blood agar Beta(β)- hemolytic Complete destruction of the red blood cells and degradation of hemoglobin Results in a clear area around the bacterial colony These bacteria produce streptolysin O or S that are responsible for the lysis. Alpha(α)-hemolytic Viridians group of streptococci Produce greenish/brownish zone around the colonies Partial hemolysis (lysis of RBCs, but not breakdown of hemoglobin Gamma(γ)-hemolytic Absence of hemolysis-no reaction surrounding the colony NOTE: Pay attention to the color of the agar where the plate has been innoculated.

Lancefield Classification Classification on the basis of immunological groups related to carbohydrate antigens associated with the cell Page 115 Separates the streptococci into groups A, B, C, D and etc.

Lancefield Classification Group A Streptococci Beta hemolytic Streptococcus pyogenes- strep throat also can cause a variety of secondary infections if strept throat is not treated Includes rheumatic fever, glomerulonephritis A certain strain of group A can be known as flesh-eating bacteria Sensitive to Bacitracin Group B Streptococci Streptococci agalactiae Can be found in the normal flora of the vaginal mucosa but can be severely harmful to babies when they are born Causes neonatal meningitis and septicemia

Lancefield Classification Group D Streptococci Alpha-hemolytic Includes many non-pathogens Enterococci Occurs in the intestinal tract Nonenterococci Streptococci bovis Found in the intestinal tract of humans and cows, sheep and other ruminants

Streptocard Acid Latex Test Rapid test for Lancefield grouping Does NOT work for Strep pneumoniae Antibody-Antigen reaction- agglutination A reagent with latex beads coated with a specific Lancefield antibody Presumably only one antibody would recognize the antigen of the Streptococcus Agglutination occurs when the antibody coated latex beads specifically bind to the specific antigen and crosslinks of multiple latex beads result Visual Clumping of the latex beads

Staphylococcus vs Streptococcus Staphylococci Occurs in clusters Catalase positive Coagulase positive Protein A - surface protein Streptococci Occurs in chains Catalase negative Lancefield Classification System